(Portions of the technical material contained in this section may not be prior art.)
The evolution of computer size now allows very small, portable, units that can be carried as personal items, for example, in briefcases, or clothing pockets. There are a variety of such devices available commercially. Among those well known in the trade are PDAs and personal PCs. For convenience, these devices are generically referred to below as PDAs.
To extend the functional capacity of these devices, many have been equipped with slots to accommodate active integrated circuit cards. These slots are commonly designated as Secure Digital or SD slots, and the cards as SD cards. When a unit is provided with I/O capability the cards are referred to as SDIO cards.
One of the widely available functions for SDIO cards is wireless LAN interfacing. These provide the PDA with a wireless connection to a WLAN network. The SDIO card in this case carries an RF integrated circuit. The card typically has digital memory circuits to implement other SDIO functions.
The combination of these circuits on a single SDIO card presents a challenge for the SDIO card design. Additional functions will be added as PDA technology develops, placing further demands on the SDIO card.
Other devices also use SD technology. Many digital cameras are provided with SD slots and cards. The SD card functions as the image storage medium. In these devices the memory circuit in the card is very large, to allow many pictures to be stored. Cell phones are also provided with SDIO capability. These are often referred to as Smartphones.
Devices that use SDIO cards are typically miniaturized, i.e. they are deliberately made small to meet market demands. Consequently, the size of the SDIO cards is small. Typical SDIO cards are approximately 1×2 inches, with a thickness less than 0.1 inch. The thickness places a major size constraint on the integrated circuit capacity of the card.